When the President signs a bill into law, he may issue a statement explaining why he is approving the legislation. These statements were traditionally brief and generally did not contain substantive analysis of the legislation. However, in recent administrations they have been used more vigorously and have become a subject of controversy. There is disagreement about their role in and importance to legislative history. See our research guide on Presidential Signing Statements for more sources and information.
The Constitution provides for Congress to appropriate money to be spent by the Federal Government, so when the White House issues the Budget of the United States in February of each year, it can be confusing. For a detailed explanation of the legislature's role in the federal budget process, see the following: CongressLine: The Budget, published on LLRX.com. You might also find useful The Essential Guide to The Federal Budget on Politico as a basic, introductory source.
For a discussion of the role of Congress in the appropriation process, versus the authorization process, see: CongressLine: Authorization and Appropriation, published on LLRX.com, or The Congressional Appropriations Process: An Introduction (CRS).
You can find out more about appropriations on Congress.gov (includes appropriations tables from ~1983-present and a variety of links to more information on appropriations and the federal budget).
Other types of material that may come out of the legislative process include committee prints and House and Senate documents. Committee prints contain information prepared for the use of the committee and sometimes include special reports or studies or compilations of earlier legislative history documents. Rarely, you might see prints that contain transcripts of markup sessions. House and Senate documents are usually of lesser importance for the purposes of legislative history research and generally contain special material prepared for Congress. These might include treaty documents, investigation reports, and reports of executive departments.
Congressional Research Service (CRS), the research arm of the Library of Congress, provides authoritative, objective, and nonpartisan research and analysis to committees and members of the House of Representatives and the Senate, regardless of party and affiliation. CRS produces new research as issues develop or are anticipated, and their reports are designed specifically to meet the needs of Congress. CRS research, while on a variety of topics, falls under five divisions: American Law; Domestic Social Policy; Foreign Affairs, Defense and Trade; Government and Finance; and Resources, Science, and Industry.